This invention is generally directed to a suspension system for a vehicle, such as, a trailer or a tractor.
A prior art suspension system currently used on trailers incorporates an equalizing toggle rocker such as the one shown in FIG. 1. The suspension system 2 is mounted on the left side of the trailer and includes a forward leaf spring 4, a rear leaf spring 6, an equalizing toggle rocker 8, a forward shackle 10 and a rear shackle 12. A front end 4a of the forward leaf spring 4 is attached to the frame 14 of the trailer at a point A. The standard equalizing toggle rocker 8 is generally triangular in shape, having a first point 8a, a second point 8b and a third point 8a. The first point 8a of the toggle rocker 8 is attached to a center frame hanger 15 which depends from the frame 14 of the trailer. The first point 8a of the toggle rocker 8 is attached to the center frame hanger 15 at a point B. A first end 10a of the forward-shackle 10 is pivotally mounted to the second point 8b of the toggle rocker 8. The first end 12a of the rear shackle 12 is pivotally mounted to the third point 8c of the toggle rocker 8. A second end 10b of the front shackle 10 is pivotally mounted to the rear end 4b of the front leaf spring 4. A second end 12b of the rear shackle 12 is pivotally mounted to the front end 6a of rear leaf spring 6. A second end 6b of the rear leaf spring 6 is attached to the frame 14 of the trailer at a point C. A front axle 16 is positioned on front spring 4 and a rear axle 17 is positioned on rear spring 6. An identical suspension system is provided on the right side of the trailer.
To the extent possible, road shock and vibrations from the tires are absorbed by the front and rear leaf springs 4, 6. Points A, B, and C are the contact points through which the road shock is passed to the frame rails 14. The fixed equalizing toggle rocker 8 induces cross forces. For example, an upward motion of the front leaf spring 4 results in a downward motion of rear leaf spring 6.
To eliminate cross forces, independent suspension systems are sometimes used on trailers. In these independent suspension systems, springs are mounted in a vertical orientation proximate each wheel. In a tandem axle suspension system, therefore, four springs are used and in a tri-axle system six springs are used. These systems attempt to absorb the road shock and vibrations experienced by each wheel by dampening the shock an vibrations with the springs. Often, however, much of the road shock and vibrations are translated to the frame of the trailer.